Adds birds to blocks in TM2020.

Particularly, the birds from MP4 will get attached to some blocks. The list of blocks is configurable.

Demo map with many birds (assuming the default block list): https://trackmania.exchange/tracks/view/213631

Warning: if a very common block (like pillars or deco walls) is selected, this can greatly impact your FPS. When I tried adding brids to grass for example, I had less than 1 FPS. The default set of blocks should be fine, but something to keep in mind.

License: Public Domain

Authors: XertroV

Suggestions/feedback: @XertroV on Openplanet discord

Code/issues: https://github.com/XertroV/tm-birds

GL HF